In the electric arc furnace (or "EAF") process used to make various grades of steel, a considerable amount of dust, known as "EAF dust," is generated. In addition to containing iron oxides derived from the steel making process, this dust also contains significant amounts of toxic substances, such as compounds of lead, cadmium, chromium, and other heavy metals. These toxic substances are contained in the dust in a potentially soluble condition, and the EAF dust thus has to be treated as a toxic material for waste disposal purposes. As is disclosed at lines 13-15 of column 1 of U.S. Pat. No. 5,278,111 of Scott W. Frame, "EAF dust is classified as a hazardous waste by the Environmental Protection Agency and is designated the identification K061."
U.S. Pat. No. 5,569,152 of Charles L. Smith, discloses that there " . . . are few effective, environmentally acceptable options for disposal of . . . hazardous waste compositions containing electric arc furnace dust . . . " (see lines 13-17 of column 1). This Smith patent teaches that the EAF dust may be fixated and/or stabilized in compositions containing lime, Portland cement, or class "C" fly ash, which are alkaline in nature but that, when such fixated and/or stabilized compositions are subjected to acid rain, the pH levels within the compositions will decrease, thereby allowing many of the heavy metals in the EAF dust (such as lead, nickel, and chromium, to be re-solubilized in water (see lines 15-25 of column 2).
The prior art also teaches that the danger from materials such as EAF dust can be substantially reduced by incorporating the materials into a vitreous composition. Thus, e.g., U.S. Pat. No. 5,273,566 of Gerald P. Balcar et al. discloses that (at lines 39-45 of column 2) "The principal danger from inorganic wastes is from heavy metal oxides and certain other oxides which may be considered `hazardous.` Heavy metal oxides readily react when exposed to strong acids or alkalies to produce soluble compounds. Vitrifying the metal oxide in a glass substantially reduces the oxides' solubility in acid." The identical disclosure also appears in U.S. Pat. No. 5,462,570 of Gerald P. Balcar et al.
The vitrification process is energy intensive and relatively expensive, and it generally produces a product whose only commercial utility is for use in an landfill. It would be desirable to be able to make a useful, salable product from the vitrified EAF dust such as, e.g., a hard abrasive.
The prior art does teach that one can make an abrasive material of unspecified properties from vitrified electric arc furnace dust. Thus, for example, at lines 32-35 of column 2 of U.S. Pat. No. 5,738,694 of George W. Ford, Jr. et al., it is disclosed that "EAF dust has also been processed by blending with silicate materials, such as silica sand, clay, or cullet, and heated in a furnace to form a vitrified ceramic product. The ceramic is useful as an abrasive . . . "
Similarly, U.S. Pat. No. 5,009,511 of Leonard S. Sarko et al. discloses a process which, according to the patentees, produces a finished product which may be used " . . . to make grinding wheels, stones, sandpaper, shot blast material, and other abrasives . . . " (see column 17, lines 4-7). As was indicated by an amendment filed in the case (U.S. Ser. No. 07/471,042) on Aug. 21, 1990, the process of this patent " . . . comprises three key steps (1) oxidation-reduction reaction, (2) blending with silicate, and (3) vitrification. The oxidation-reduction reaction is necessary in order to place the inorganic hazardous waste components into a form for chemical reaction. The blending step is necessary to intimately mix the oxidation-reduction product with the silicates so as to ensure a complete reaction of the inorganic hazardous waste components with the silicates. The vitrification step is necessary in order to effect the chemical reaction which will chemically bind the inorganic hazardous waste components to the silicate matrix. These steps must be carried out in the aforementioned order . . . "
However, the aforementioned Balcar et al. patents teach that one cannot make a hard abrasive from vitrified oxide-containing material, such as vitrified EAF dust. Thus, e.g., in the section of Balcar et al.'s U.S. Pat. No. 5,273,566 starting at line 66 of column 2 (and extending to line 5 of column 3), Balcar et al. discuss U.S. Pat. No. 5,009,511 of Sarko et al. and state that "The Sarko et al. reference teaches a mobile system for fixing a hazardous waste in a silicate matrix . . . Although this reference teaches a vitrification process for disposal of hazardous wastes, it is directed to stabilizing those wastes in a silicate matrix. Further, while this type of material is acceptable for use in stabilizing wastes, it is inappropriate for fabrication of a high hardness, abrasive material."
The Balcar et al. U.S. Pat. No. 5,273,566 was issued in 1993. However, for many years prior to such issuance, it was widely known that vitreous materials were not suitable for making high hardness abrasive materials. Thus, for example, in 1964 U.S. Pat. No. 3,156,545 issued to Samuel S. Kistler et al. This patent disclosed (at lines 21-26 of column 2 ) that "It is well known that glassy materials are fragile and readily susceptible to fracture and disintegration and at least partially for this reason, the abrasive industry has intentionally avoided glassy compositions in abrasive grains up to the present time." Thus, by way of yet another example, in 1931 U.S. Pat. No. 1,830,757 issued and disclosed that glass is a "comparatively weak non-abrasive particle."
It thus is an object of this invention to provide a process for preparing an abrasive composition made from EAF dust which is environmentally safe and, additionally, does not exceed the United States Environmental Protection Agency's Leaching Procedure regulatory limits.
It is another object of this invention to provide a process for preparing an abrasive composition which is economical to produce.
It is another object of this invention to provide a process for preparing an abrasive composition with good hardness and fracture toughness properties.
It is yet another object of this invention to provide a process for preparing an abrasive composition which is effective. As is known to those skilled in the art, the mere fact that a material might have good hardness and fracture toughness properties does not necessarily mean that it will be a good abrasive. Thus, as is disclosed at page 5 of Richard L. McKee's "Machining With Abrasives (Van Nostrand Reinhold Company, New York, N.Y., 1982), "It has been observed that all abrasives are hard, but not all hard substances are abrasive. Indeed, there are several materials which are harder than either silicon carbide or aluminum oxide, but no so abrasive. Other factors than relative hardness enter into the picture in determining which abrasives to use on what materials. Diamond is harder than CBN, and more effective on carbides, but less effective on steels . . . Aluminum oxide is more effective on most steels and less so on nonferrous metals and nonmetallic substances than is silicon carbide. The best explanation of the problems of diamond an silicon carbide on steel is that there is a chemical reaction between the abrasive and the steels which in effect `melts` the abrasive and causes excess wear."